Earth Science

Earth as a Planet

Earth’s Layers

Study Tip
Just like the spherical layers in an onion, the Earth has multiple layers that serve different purposes.

Layers by Composition

  • The crust is less than 1% of Earth by mass. The two types are oceanic crust and continental crust.
  • The mantle is hot, ultramafic (filled with magnesium and iron) rock. It represents about 68% of Earth's mass.
  • The core is mostly iron metal. The core makes up about 31% of the Earth.
Study Tip
Just like the spherical layers in an onion, the Earth has multiple layers that serve different purposes.

Layers by Mechanical Properties

  • The lithosphere is composed of both the crust and the portion of the upper mantle and behaves as a brittle, rigid solid.
  • The asthenosphere is partially molten upper mantle material and behaves plastically and can flow.
cross section of Earth
A cross section of Earth showing the following layers:
(1) crust (2) mantle (3a) outer core (3b) inner core (4) lithosphere (5) asthenosphere (6) outer core (7) inner core
Concept Check
  • How can the Earth be divided into layers by composition?
  • How can the Earth be divided into layers by mechanical properties?